By David Lawder and Humeyra PamukWASHINGTON, Aug 24 (Reuters) - President Donald Trump's administration on Monday announced a possible expansion of sanctions on countries doing business with Iran as part of what it billed as an "economic D-Day," but stopped short of actually imposing penalties.As the war with Iran nears its six-month mark, Treasury Secretary Scott Bessent said the U.S. was launching an "economic onslaught" against Iran's financial connections around the globe.

President Donald Trump announced this week that the U.S. would be imposing an “unprecedented” level of economic warfare and isolation on Iran.

The Trump administration calls this "economic D-Day" on Iran. Iran vows to respond to fresh sanctions in a "seismic manner."

The Trump administration has expanded its secondary sanctions against entities and countries doing business with Iran, warning them to cut ties with Tehran or risk losing access…